Don, I actually agree with most if not all your points..
In our dojo we sometimes before or after class we do a bit of "practical applications", basically, just fooling around while waiting for everyone to arrive. in a way, it's a bit of like sparing.. Its just not part of the curriculum.
Its just that whenever I "win" its just that i get the feeling its because im stronger or bigger than my partner, and when I lose, its because my partner is stronger or bigger than me..
It makes it hard for me to evaluate the benefits of sparing when my own experience of it has yet to show me any..
Or they are there, I haven't yet discovered them..
The trick in that situation is to look at it constructively. How did the bigger guy beat you? How did you win against a smaller guy? Was it just strength? Was it good technique? What could be done to cope with how you were beaten? How can you practice the methods required to cope with the reason you were beaten?
To beat someone smaller then you with strength is easy. To beat someone smaller then you with strength when the small guy has good technique is harder. To beat someone smaller then you without using strength is very hard. If you are constantly beating someone because you are bigger, try not using strength and focus in on your technique. If you are being beaten by guys bigger then you, learn from it. Focus on techniques that take advantage of their size.
I have an old saying I tell new guys in my club. "Don't pull guard on a fat guy." It's another way of saying the situation dictates the tactics, not the other way around.
And sure, it all sounds very easy to say on a forum. In practice it takes a LONG time to get good at. I sparred 4 days a week for a year before I ever tapped anyone bigger/stronger then me. I know a 15 year old kid in our club who can put the hurting on most adults of any size in bjj, myself included. He knows how to play to his advantages (crazy flexibility and speed). I think he is about 115 pounds.
In the end it comes down to looking at it from a 3rd party viewpoint. You have to be honest. If you are told a technique works on bigger stronger attackers, and you can't seem to get it to work in sparing, you have to ask why?
Is the problem you? Is the problem the technique? Is the problem somewhere in between?
I keep a notebook log of all my sparing and training. I use it to keep tabs on what I need to work on and how I feel about what I've done. I highly recommend that, and asking your instructor for some insight into why what you are trying to do just isn't working like you think it should.